Label on edges with tikz-graph

I would like to add a label to some of my edges in a tikz-graph.

I have tried the code below, but it adds the label to the parent node - I would like this label to be on the edge instead.

\documentclass{article}
\usepackage{pgf}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{arrows,shapes,snakes,automata,backgrounds,petri}
\usetikzlibrary{positioning}
\usetikzlibrary{graphs}
\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs}
\usegdlibrary{layered}

\begin{document}
\begin{figure}
\begin{center}
\tikz [baseline=(current bounding box.center)] \graph [layered layout, grow'=right, level sep=1cm, sibling distance=.5cm] {
toto [label=mylabel] ->  {
a,b
}
};
\end{center}
\end{figure}
\end{document}


Result :

Does anyone know how could I get the label on the arrow instead ?

I have also tried this, which did not compile (in lualatex):

\documentclass{article}
\usepackage{pgf}
\usepackage{tikz}
\usepackage{pgfplots}
\usetikzlibrary{arrows,shapes,snakes,automata,backgrounds,petri}
\usetikzlibrary{positioning}
\usetikzlibrary{graphs}
\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs}
\usegdlibrary{layered}

\begin{document}
\begin{figure}
\begin{center}
\tikz [baseline=(current bounding box.center)] \graph [layered layout, grow'=right, level sep=1cm, sibling distance=.5cm] {
toto ->  {
a,b
};
\draw (toto) edge node{label} (a);
};
\end{center}
\end{figure}
\end{document}


First of all, it seems that you need a quite bleeding edge Tikz to make this work. But I found the solution on the section 19.2.3 of the tikz-pgf 3.0.0 manual:

add \usetikzlibrary{quotes} in the preamble and then:

\tikz [baseline=(current bounding box.center)] \graph [layered layout, grow'=right, level sep=1cm, sibling distance=.5cm] {
toto  ->  [red] { % apply to all the edges
a [> "lab1"], b [> {blue, sloped, pos=0.9, "lab2"'} ]  % apply only to the edge to this node with the ">"
}
};


will produce:

...don't ask for the strange value of pos, I found it by trial and error.

• Thanks ! By tweaking the value of pos and also changing a bit the value of sibling distance to give some breathing space, I've been able to obtain a nice one ;-) – potterman28wxcv May 27 '16 at 11:39
• Note the ' that brings the label below the edge :-D – white_gecko Feb 6 at 23:11